There is known a vehicular power transmitting system including a power distributing device which distributes a drive force produced by a main drive power source to a first electric motor and a power transmitting member, a second electric motor connected through a step-variable transmission to a power transmitting path between the power transmitting member and a vehicle drive wheel, and an electric-energy storage device which stores an electric energy generated by the first and second electric motors and supplies the electric energy to the first and second electric motors. Regarding such a vehicular power transmitting system, there has been proposed a technique wherein a torque-reduction control is implemented to reduce an output toque of the second electric motor during a shifting action of the step-variable transmission, and an amount of reduction of the output torque of the second electric motor during the torque-reduction control is limited according to an amount of limitation of charging and discharging of the electric-energy storage device. Patent Document 1 describes an example of such a power transmitting system. According to this technique, a lower limit of the output torque of the second electric motor calculated on the basis of target speed and torque values of the first electric motor is limited by a lower-limit limiting value of the second electric motor calculated on the basis of an input limit value of the electric-energy storage device, for reducing a shifting shock upon a shifting action of the step-variable transmission while effectively preventing an overcharging of the electric-energy storage device.    Patent Document 1: JP-2005-297948 A    Patent Document 2: JP-2002-225578 A
In the prior art technique, however, the torque reduction control (amount of reduction of the torque) of the second electric motor is limited while the input to the electric-energy storage device is limited, giving rise to a risk of generation of a shifting shock due to a delay of the shifting action of the step-variable transmission which is caused by an insufficient engaging force of a frictional coupling element incorporated in the step-variable transmission under some condition of the vehicle. In view of this drawback, there has been a need for developing a control apparatus for a vehicular power transmitting system wherein an electric motor is connected through a step-variable transmission to a drive-wheel-side output shaft to which a drive force of a main drive power source is distributed by a power distributing device, which control apparatus is configured to reduce a shifting shock upon a shifting action of the step-variable transmission.